Sensor system

ABSTRACT

Sensor system comprising a frame supporting a force-sensing tip arranged to generate a signal based upon a force applied by said force-sensing tip to a material to be tested, the system further comprising:
         an input drum mounted in said frame such that it can rotate about an input axis of rotation;   an output lever supported by said frame by means of an output revolute joint defining an output axis of rotation;
 
wherein said force-sensing tip is mounted on said output lever such that said force-sensing tip is arranged to be brought into contact with a material to be tested;
 
and wherein said sensor system comprises a mechanical transmission arranged to kinematically link said input drum to said output lever such that a rotation of said input drum about said input axis of rotation causes said output lever to pivot in an oscillatory manner about said output axis of rotation.

TECHNICAL FIELD

The present invention relates to the technical field of sensor systems.More particularly, it relates to a force sensor for measuring smallforces applied to materials, particularly but not exclusively tobiological tissues.

STATE OF THE ART

The human ear consists of three parts: the outer ear (ear canal andeardrum), the middle ear (auditory tube and the three ossicles) and theinner ear (see FIG. 1). The sound wave passes through the ear canal andvibrates the tympanic membrane. The movement of the eardrum is thentransmitted by the ossicles to the inner ear before being transformedinto electrical signals.

Some diseases are responsible for the partial or total destruction ofossicles (e.g. ear infections and cholesteatoma) or loss of mobility(e.g. otosclerosis). These pathologies of the middle ear lead to ahearing loss.

A decrease in sound perception may also be due to a dysfunction of theinner ear. Doctors use hearing tests or complementary examinations (MRI,verification of the ossicular chain mobility) to establish a completediagnosis.

In case of middle ear surgery, the surgeon may have to replace one ormore elements of the middle ear with prostheses. During the operation,the skin at the base of the tympanic membrane is incised and lifted toprovide access to the middle ear. The surgeon applies forces to evaluatethe stiffness and mobility of the ossicular chain). This information canbe used per-operatively to qualify and quantify the disease andtherefore determine the best cure, as well as to validate surgicalprocesses and related outcomes. Once the prosthesis is installed, thesurgeon follows the same approach to check the ossicular chain mobilityto ensure that the placement was correctly performed.

The PalpEar, developed by Sensoptic, is described in the patentEP2626680, and is illustrated in the lower part of claim 3. This deviceis a tool for middle ear surgery with an optical force sensor integratedtherein, used as illustrated in FIG. 2. A standard 45° Storz tip (seethe upper device on FIG. 3) is combined with a triaxial optical sensorused to measure the force applied by the surgeon at the end of the tool.The surgeon can thus rely on this feedback to estimate the level ofmobility of the ossicles.

However, the disadvantage of this system is the lack of information onthe displacement generated during palpation. The notion of mobilityremains a subjective assessment from the surgeon especially as thedisplacement to be generated (of the order of several microns) and theforce to be measured range (mN) are close to the limit of, or are evenbeyond, human (surgeon) capabilities.

An aim of the present invention is hence to at least partially overcomethe above-mentioned drawbacks of the prior art.

DISCLOSURE OF THE INVENTION

More specifically, the invention relates to a sensor system as definedin claim 1. This sensor system comprises a frame (e.g. a hollow tubularframe) supporting a force-sensing tip arranged to generate a signalbased upon a force applied by said force-sensing tip according to one,two or three axes.

According to the invention, the system further comprises:

an input drum mounted inside said frame such that it can rotate about aninput axis of rotation;

an output lever supported by said frame by means of an output revolutejoint (which may be for instance a pinned hinge joint or a flexure pivotsuch as a remote centre compliance RCC pivot) having one degree offreedom in rotation and hence defining an output axis of rotation whichis ideally perpendicular to said input axis of rotation.

Said force-sensing tip is mounted on said output lever such that saidforce-sensing tip, particularly a distal extremity thereof, is arrangedto be brought into contact with a material to be tested, for instance abiological material such as an ossicle.

Furthermore, said sensor system comprises a mechanical transmissionarranged to kinematically link said input drum to said output lever suchthat a rotation of said input drum about said input axis of rotationcauses said output lever to pivot in an oscillatory manner (i.e. backand forth) about said output axis of rotation.

As a result, by pivoting said input drum, a predetermined displacementof the distal extremity of the tip is generated, with a precise, knownrelationship between the input rotation and the output displacement. Asa result, the user can calculate the resistance of the material on thebasis of the known displacement of the distal extremity of the tip andthe force measured by the tip rather than having to rely on feel andperception alone. This system is applicable more widely than simply formeasuring the movement and resistance of ossicles, e.g. for hardnessmeasurement of soft materials such as elastomers, rubbers, gels and soon.

Specific realisations and other advantageous details are described inthe dependent claims, which can be combined in any manner which makestechnical sense.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the invention will appear more clearly upon readingthe description below, in connection with the following figures whichillustrate:

FIG. 1 is an illustration of the anatomy of a mammalian, in this casehuman, ear;

FIG. 2 is an illustration of the use of the PalpEar device;

FIG. 3 is an illustration of a conventional Storz-type hook and aPalpEar device for testing the properties of body tissues, particularlyear tissues, more particularly ossicles;

FIG. 4 is a partial schematic diagram of a first embodiment of a sensorsystem according to the invention;

FIG. 5 is a partial schematic diagram of a second embodiment of a sensorsystem according to the invention; and

FIG. 6 is a partial schematic diagram of a third embodiment of a sensorsystem according to the invention.

EMBODIMENTS OF THE INVENTION

FIG. 4 illustrates schematically a first embodiment of a sensor system 1according to the invention, which clearly illustrates the kinematicsupon which the device of the invention is based. The sensor system 1 isarranged to measure the force applied to a material in response to adisplacement, this material being in particular a biological tissue,more particularly ossicles. However, the system 1 is applicable morewidely, e.g. for hardness testing of soft materials such as rubbers,elastomers, gels and so on.

The device comprises a frame 306, illustrated here in the form of acylindrical hollow tube. This frame 306 supports an input drum 301 byany convenient means (e.g. interior flanges 306 a in the illustratedcase), which is arranged to be driven about a first (input) axis ofrotation A either mechanically, hydraulically, pneumatically ormanually. This first axis A is coincident with the longitudinal axis ofthe frame 306, but this does not strictly have to be the case, the firstaxis A being offset therefrom linearly and/or angularly. The input drum301 interacts with an off-centre (i.e. eccentric) pin 302 which may befixed thereto or, as illustrated, be provided linked thereto via acylindric joint. The pin 302 hence follows a rotary trajectory relativeto the frame 306, orbiting around the axis A in a plane perpendicularthereto. A universal joint 303, 304 of any convenient type is providedbetween the off-centre pin 302 and a substantially rigid connectinglever 305, this latter being itself linked to an output lever 309 bymeans of a revolute connecting joint 307 such as a simple pinned jointas illustrated. This joint 307 defines a second (intermediate) axis ofrotation B which is perpendicular to the first axis of rotation A. Itshould be noted that, alternatively, the off-centre pin 302 can be fixedto (or even monobloc with) the drum 301 and fitted with play or via acylindric or other resilient joint into a corresponding opening in anelement of the universal joint 303, 304.

The elements numbered 302, 303, 304, 305 and 307 hence constitute amechanical transmission between input drum 301 and output lever 309,kinematically linking these two elements.

The output lever 309 is arranged to have one degree of freedom inrotation by being pivoted on the frame 306 by means of an outputrevolute joint 308, here illustrated as a pin which extendsdiametrically across the frame 306 so as to define a third (output) axisof rotation C which is perpendicular to the first axis of rotation A andto the second axis B. However, as will be seen below in the context ofFIGS. 5 and 6, other types of revolute (i.e. one degree of freedom)joints are possible.

As a result, a rotation of the input drum 301 causes the output lever309 to pivot back and forth about the third axis of rotation C withinpredefined angular limits and in a plane perpendicular to axis C.

Output lever 309 is provided with a force-sensing tip 110 e.g. of thetype described in EP2626680 and EP2255170 (hereby incorporated byreference in their entireties) or any other convenient type (mechanical,piezoelectric, optical or similar, arranged to output an electrical,optical or other signal based on a force applied by or to said tip 310according to one, two, three or more axes), which is arranged to bebrought into contact with a material to be measured, such as but notlimited to biological tissue, particularly ear tissue, more particularlyossicles in order to measure the resistance force generated in responseto displacement of the tip 310 when it is brought into contact with thematerial in question. For ossicle-related measurements, a 0-100N,ideally 0-0.5 N measuring range with a resolution of e.g. 5 mn, ideally2 mN is appropriate.

For small angular displacements of the output lever 309 around thirdaxis C for which the small-angle-approximation holds (i.e. approximately±12° either side of the first axis A), the distal end 311 of the tip 310is substantially linear.

Since there is a kinematic, and indeed desmodromic relationship betweenthe input drum 301 and the distal end 311 of the tip 310, a known inputrotation of the drum 301 (measured e.g. by a well-known rotary encoderor similar) will cause a known substantially linear displacement of thedistal end 311 in a plane parallel to axis A and perpendicular to axisC. As a result, the displacement of the distal end 311 of the tip 310can be precisely known based on the rotational input to the drum 301.

It should be noted that the output lever 309 and/or the tip 310 can besealed to the frame 306 by a seal of any convenient type (notillustrated) if required.

Since the diameter of the frame 306 may be very narrow, e.g. of theorder of 2 mm in the case in which the sensor 1 is arranged to be ableto be inserted into a human ear, the universal and pinned jointsillustrated in FIG. 4 may not be appropriate in certain situations sincethey may be difficult or impossible to construct for manufacturingreasons.

FIGS. 5 and 6 illustrate schematically partial views of advantageoussolutions to this issue, based around micromachining and/or additivemanufacturing, e.g. using femto laser printing technology or otheradditive manufacturing techniques. Since little assembly is required,this significantly reduces the cost of the sensor 1, and also allows toreach a suitable system dimension (diameter <2 mm) for intra-aural use.The embodiments illustrated in these figures will be described belowonly insofar as they differ from that of FIG. 4.

In each of FIGS. 5 and 6, the connecting lever 305 is not present, andoutput lever 309 is pivoted on frame 306 by means of a flexure pivotsystem 308. Such pivots are described e.g. in “The Art of FlexureMechanism Design”, Florent Cosandier, Simon Henein, Murielle Richard andLennart Rubbert, EPFL Press, 2017 (hereby incorporated by reference inits entirety), and typically comprise mechanisms constructed of flexuresof the blade spring type, cols, torsion rods and so on. This flexurepivot 308 may be monobloc with the output lever 309, or this latter maybe fixed thereto e.g. by force fitting, bonding, welding or similar.

In FIG. 5, the flexure pivot 308 defines revolute joint a one degree offreedom around axis of rotation C, which is formed as a Remote CentreCompliance (RCC) pivot which defines said axis C. To this end, the pivot308 comprises a pair of blade springs 308 a, 309 a which, whenunstressed, extend in respective planes parallel to the axis of rotationC and which intersect this latter.

In this embodiment, the input drum 301 (illustrated also in plan view atthe top of the figure) comprises an internal cam surface 301 a, and theoutput lever 309 further comprises a cam follower 312 which ismaintained in contact with the cam surface 301 a by means of apre-stress of the flexure pivot 308. The mechanical transmissionconstituted by cam surface 301 a and cam follower 312 is hence kinematicbut not desmodromic in this case.

Cam follower 312 can be monobloc with the output lever 309 or a separatepart fixed thereupon. In essence, this latter is constructed such that,in the absence of the input drum 301, the output lever 309 would beinclined at a greater angle to the first axis A than is illustrated. Theflexure pivot 308 is hence arranged to bias the output lever 309 suchthat the cam follower is biased against the can surface 301 a. Camsurface 301 can be of any convenient form, such as oval, polygonal, orwith any convenient number of lobes (six are illustrated in FIG. 5, butthe number can be two, three, four, five, six, seven, eight or evenmore). Alternatively, the input drum can have an exterior cam surface,the shape of the output lever 309 and the cam follower 312 being adaptedin consequence. In either case, the input drum 301 can be offset suchthat the input axis A does not intersect the output axis C.

As a result, rotation of the input drum 301 causes the distal end 311 ofthe tip 310 to displace back and forth in its plane as described in thecase of FIG. 4, this displacement being known based on the angulardisplacement of the input drum as before.

In the embodiment of FIG. 6, the input drum 301 comprises an eccentricpin 302 arranged facing the tip 310, as in FIG. 4. The pivot arrangementdefining the axis of rotation C is as in FIG. 5, and need not bedescribed further. In this embodiment, the universal joint 303, 304 theconnecting rod 305, the revolute joint 307 (which defines second axis ofrotation B), the output lever 309 and the flexure pivot arrangement 308(defining axis of rotation B) are of monobloc construction. Theuniversal joint 303, 304 is formed as a pair of col (notch) or bladeflexures arranged to act at 90° to one another, a first flexure 303arranged to permit bending parallel to axis C, the second flexure 304arranged to permit bending perpendicular thereto. It does not matterwhich of flexures 303 and 304 is closest to the input drum 301.

Indeed, the flexure nearest the pin 302 can be arotationally-symmetrical hour-glass shaped col with two degrees offreedom in bending.

The pin 302 is either fixed to the drum 301 and situated with play in ahole in the universal joint 303, or vice-versa.

Revolute joint 307 is again formed as a col or blade flexure so as toprovide a degree of freedom in rotation in a plane perpendicular to axesA and C.

The embodiment of FIG. 6 hence acts in the same manner as that of FIG.4, the pinned pivots having been replaced by equivalent flexure pivots.

The stroke and frequency of the distal end 311 of the tip 310 can beadjusted according to the surgeon's needs in order to apply anappropriate displacement, for instance by positioning the body 306 andthe distal end 311 of the tip 310 as required and rotating the inputdrum 301 by an appropriate angle at an appropriate speed. The maximumstroke of the end 311 can be predetermined at manufacture by acting uponthe lengths of the levers 305, 309, the position of the various pivots303, 304, 307, 408 and the radial position of the pin 302 on the inputdrum 301 or the shape of the cam surface 301 a as appropriate.

A safety system can be also arranged to ensure that no damage is causedto the material under test by preventing application of excessive forceby the tip 310. Such a security system can for instance be achieved byintegrating a bi-stable mechanism at the tip 110 which will cause thetip 110 to “spring” backwards in the case of excessive force beingapplied. Alternatively, a friction clutch, slip joint or similar can beplaced so as to cause the tip 110 to “give” and displace with regard tothe output lever 309 once a certain force has been exceeded.

Although the invention has been described in respect of specificembodiments, variations thereto are possible without departing from thescope of the appended claims. For instance, where certain axes ofrotation have been described as being perpendicular to one another, thisdoes not necessarily have to be so in situations in which suchnon-perpendicular axes will function adequately.

1. Sensor system comprising a frame supporting a force-sensing tiparranged to generate a signal based upon a force applied by saidforce-sensing tip to a material to be tested, said system furthercomprising: an input drum mounted in said frame such that it can rotateabout an input axis of rotation; an output lever supported by said frameby means of an output revolute joint defining an output axis ofrotation; wherein said force-sensing tip is mounted on said output leversuch that said force-sensing tip is arranged to be brought into contactwith a material to be tested; and wherein said sensor system comprises amechanical transmission arranged to kinematically link said input drumto said output lever such that a rotation of said input drum about saidinput axis of rotation causes said output lever to pivot in anoscillatory manner about said output axis of rotation.
 2. Sensor systemaccording to claim 1, wherein said mechanical transmission comprises aconnecting lever arranged to interact with the input drum at a point onsaid input drum which is eccentric with respect to the input axis via auniversal joint having two degrees of freedom in bending, and which ispivotally connected to said output lever via a revolute connecting jointdefining an intermediate axis of rotation which is situated in a planeparallel to the input axis and perpendicular to the output axis. 3.Sensor system according to claim 2, wherein said connecting lever, saiduniversal joint and said output lever are monobloc.
 4. Sensor systemaccording to claim 2, wherein at least one of said universal joint andsaid revolute connecting joint comprise at least one flexure pivot. 5.Sensor system according to claim 4, wherein both of said universal jointand said revolute connecting joint comprise at least one flexure pivot.6. Sensor system according to claim 1, wherein said input drum comprisesa cam surface, and wherein mechanical transmission comprises a camfollower integrated with said output lever, said cam follower beingmaintained in contact with said cam surface.
 7. Sensor system accordingto claim 6, wherein said cam follower and said output lever aremonobloc.
 8. Sensor system according to claim 1, wherein said outputrevolute joint is a defined by a flexure pivot system such as a remotecentre compliance pivot.
 9. Sensor system according to claim 8, whereinsaid flexure pivot system and said output lever are monobloc.
 10. Sensorsystem according to claim 1, wherein said frame is adapted to behand-held.
 11. Sensor system according to claim 10, wherein said frameis substantially tubular.
 12. Sensor system according to claim 11,wherein said frame has a diameter of 3 mm or less.
 13. Sensor systemaccording to claim 12, wherein said frame has a diameter of 2 mm orless.
 14. Sensor system according to claim 1, further comprising a forcelimiter adapted to prohibit application of an excessive force to saidmaterial by said tip.
 15. Sensor system according to claim 1, whereinsaid sensor system is adapted for making measurements of biologicaltissue.
 16. Sensor system according to claim 15, wherein said sensorsystem is adapted for intra-aural use.
 17. Sensor system according toclaim 16, wherein said material is an ossicle.